Environmental regulations may limit the amount of NOx emitted from turbine engines. One known manner for reducing NOx emissions is to mix the compressed air used for combustion with fuel before the air enters the primary combustion zone. Such premixed air burns cleaner than combustion air that is not premixed so as to reduce the amount of NOx generated. In addition to the NOx reduction benefit, premixed combustion air can assist in the management of the dynamic forces during combustion. In particular, when the primary combustion zone is provided with a air/fuel premixture, a more stable, controlled and predictable combustion occurs. As a result, the potential for high frequency acoustic combustion forces and their associated dangers are minimized.
A fuel injector assembly can be provided for distributing fuel into the compressed air flow upstream of the main combustor portion of the turbine. In one prior design, fuel is injected into the compressed air stream using a ring-type assembly 90 as shown in FIG. 2A. The prior fuel ring assembly 90 includes a fuel ring 95, a fuel supply tube 100 and five attachment legs 150.
The configuration of the prior fuel supply tube 100 is shown in FIGS. 5A and 5B. The prior fuel supply tube 100 comprises an elongated body 102 having first and second ends 104, 106. The elongated body 102 has a generally tapering cylindrical outer profile. Extending longitudinally through a portion of the elongated body 102 is a circular passage 108 through which fuel can flow. The circular passage 108 begins at the second end 106 of the supply tube 100 but does not extend through to the first end 104. The first end 104 of the supply tube 100 includes a circular passage 110 that extends from a connection interface surface 112 and partially into the first end 104 and substantially transverse to the circular passageway 108 of the elongated body 102 such that the circular passages 102, 110 are in fluid communication. Though the exterior of the supply tube 100 is tapered, the circular passage 108 maintains a substantially constant diameter through the elongated body portion 102.
The connection interface 112 of the tube 100 can connect into a fuel supply source or conduit (not shown); the second end 106 of the tube 100 can be connected to the fuel ring 95. The fuel ring 95 (see FIG. 2A) includes a hollow interior such that the passages 108,110 in the supply tube 100 fluidly communicate with the hollow interior of the fuel ring 95. In particular, the supply tube 100 is connected into the fuel ring 95 so that it extends substantially perpendicular from the fuel ring 95. Further, the supply tube 100 is connected to the fuel ring 95 such that the center line of the passage 108 in the elongated body 102 is in line with the hollow interior of the fuel ring 95. In other words, the center line of the elongated body 102 of the supply tube 100 is not offset from the hollow interior of the fuel ring 95.
In addition to the details of the prior supply tube 100, the configuration of the prior attachment legs 150, as shown in FIGS. 3A and 3B, deserves mention. The prior attachment legs 150 include a first end 152, a second end 154 and a substantially planar bridge portion 156 connecting the first and second ends 152,154. The first end 152 includes a portion 158 that protrudes transversely outward from the bridge portion 156. The first end 152 further includes a passage 160 for receiving a bolt. The second end 154 includes a c-shaped portion 162 that protrudes transversely outward from the bridge portion 156 of the attachment leg 150. Further, the c-shaped portion 162 extends in the opposite direction of the protruding portion 158 of the first end 152.
While the above-described prior fuel ring configuration has proved successful in combination with certain turbine engine designs, it has been difficult to integrate it into more recent turbine engine designs because of structural interferences with nearby components. However, it is still desirable to retain the fuel ring due to the various benefits of premixed combustion air as discussed above.
Thus, one object according to aspects of the present invention is to provide a new configuration for a turbine fuel ring assembly that avoids interferences with adjacent turbine engine structure. Another object according to aspects of the present invention is to provide an improved attachment leg for the fuel ring assembly that not only avoids interferences but also provides enhanced stress distribution characteristics. Yet another object according to aspects of the present invention is to provide a fuel supply tube that uses differing flow passage conformations to allow the exterior of the tube to avoid interferences while maintaining relatively constant flow area. Still other aspects according to the present invention relate to retrofitting prior engines with the present fuel ring assembly without extensive rework or retrofit operations. These and other objects according to aspects of the present invention are addressed below.